1. Field of the Invention
This invention relates to a method of adjusting an implantable cardiac stimulator or pacemaker from outside the patient's body; a programmer, on the one hand and a cardiac stimulator, on the other hand, for carrying out the method; and the functionally unitary assembly comprising the stimulator and the programmer.
2. Description of the Prior Art
Methods of adjusting an implantable and adjustable cardiac stimulator through means located outside the patient's body are already known in the art. This heart stimulator comprises a probe electrically connected to a case containing: a source of electric current; an amplifier and a filter; a logic module of which the function consists in generating stimulating pulses; an output stage capable of feeding calibrated pulses to the probe; and, finally, a flexible-blade switch normally urged to its open-circuit position and adapted to be short-circuited when exposed to a magnetic field, notably of extra-corporeal origin. The function of the magnetic switch is to control the programme of operation of the logic module, notably a general programme in which the cardiac stimulator operates as a "demand" unit, and a particular programme.
In the first known method of adjusting the implantable cardiac stimulator a permanent magnet is brought close to the site where the stimulator is inserted, so as to short-circuit the magnetic switch and thus start a particular logic programme describing sequentially the various conditions of the adjustable characteristic to be programmed. When the desired specific value is attained, the magnet is removed so that the magnetic switch will resume its open position and the cardiac stimulator operates normally according to the demand with the characteristic at the programmed value. This method is advantageous in that the apparatus required outside the patient's body is particularly small (permanent magnet). However, it is objectionable in that it is difficult to carry out since the magnet must be removed quickly at the proper time. Moreover, with this method only one and single characteristic of the stimulator can be adjusted.
In a second known method an electromagnet located outside the patient's body is used close to the location where the cardiac stimulator or pacemaker is inserted. The electromagnet coil is controlled in such particular way that a pulsating magnetic field is created, in order to open and close the magnetic switch according to a particular mode corresponding to a coded information processed by the logic module determining which is the characteristic to be adjusted on the one hand and the adjustment value of this value on the other hand. It can be said to the credit of this method that is permits a polyvalent adjustment. However, the degree of safety is far from perfect since on the one hand only one control action is performed and on the other hand the programmer cannot control the accuracy with which the data are taken into account by the stimulator.
In a third known method a high-frequency electromagnetic emission modulated both in frequency and amplitude is transmitted through extra-corporeal means. This emission is collected by an implanted antenna so as to be detectable. With this method it is also possible to cause the variation of several adjustable characteristics of a stimulator. However, with this third method the stimulator must be modified since it requires the incorporation of means for receiving the electromagnetic emission.
From the foregoing it is clear that these known methods are either limited as to their field of application, or difficult or awkward to use, or rather unreliable, or require a specific transformation or conversion of the cardiac stimulator or pacemaker.